Future generations of dielectric films utilize porogens in combination with organosilicates precursors to produce porous low k films. For this purpose saturated or unsaturated hydrocarbon-based porogens are co-deposited with the organosilicate to produce the initial composite film, comprising a mixture of organosilicate precursor and organic porogen. This film is subsequently subjected to various treatment methods to decompose the porogen. During this curing process the porogen byproducts are liberated as gaseous species leaving behind an organosilicate matrix containing voids in the spaces vacated by the porogen. The resulting voids or air pockets have an intrinsic dielectric constant of unity which has the effect of decreasing the overall dielectric constant of the porous solid below that of the dense matrix material.
Other areas in which organic precursors are being used in the microelectronics industry are the deposition of carbon hardmasks and the deposition of anti-reflective coatings. These films are deposited by plasma enhanced chemical vapor deposition (PECVD) using hydrocarbon precursors, especially unsaturated organic hydrocarbons.
Unsaturated hydrocarbon-based materials have been evaluated for use as a porogen precursor to be used along with an appropriate organosilicate precursor for the deposition of porous low k films.
However, many unsaturated hydrocarbons that are prone to polymerization will gradually degrade or polymerize at ambient temperature or at moderate temperatures that are often encountered during normal processing, purification or application of the particular chemical. The prior art discloses a variety of chemicals used to stabilize hydrocarbon-based porogens against the polymerization of olefinic hydrocarbons, including several broad classes of organic compounds such as phenols, amines, hydroxylamines, nitro compounds, quinine compounds and certain inorganic salts. An example of this would be monomers such as butadiene and isoprene which are well known to undergo gradual polymerization in storage tanks or during transportation at ambient temperatures.
Some of unsaturated hydrocarbon-based precursor materials are described in U.S. Pat. No. 6,846,515, commonly assigned to the assignee of the present invention, which is incorporated by reference herein in its entirety.
2,5-Norbornadiene (NBDE) is one of the leading materials being evaluated as a precursor for porogen, carbon hardmask and antireflective coating, for the production of low dielectric constant films using chemical vapor deposition (CVD) methods. Isoprene is a promising precursor for the deposition of carbon hardmasks and antireflective coatings. However, NBDE and isoprene are thermally unstable with respect to oligomerization/polymerization.
NBDE and isoprene degrade at a substantial rate at ambient temperature to form soluble NBDE and isoprene oligomeric degradation products. Isoprene is also known to undergo a relatively rapid dimerization reaction. Hence, the concentration of dissolved oligomers in NBDE and isoprene are expected to gradually increase over time during their transport and storage prior to their utilization as a precursor for dielectric materials. Furthermore, the soluble oligomers will immediately precipitate upon contact with a more polar liquid such as diethoxymethylsilane (DEMS). This instability is expected to cause precursor delivery problems and film quality issues.
Chemical vendors commonly supply NBDE with 100-1000 parts per million (ppm) of 2,6-di-tert-butyl-4-methylphenol, also known as butylated hydroxytoluene or by the acronym BHT. BHT is currently used as the industry standard to slow the rate of NBDE degradation for transport and storage purposes. However, BHT has limited efficacy to suppress NBDE degradation.
A recently published US Patent Application 20070057235 by Teff et al. taught the use of phenolic antioxidants for the stabilization of NBDE.
In order for NBDE or isoprene to be viable in a manufacturing environment it is critical that the oligomer (i.e., non-volatile residue) content is minimized to avoid processing issues and to allow manufacturers to meet the demanding film quality specifications as set by the semi-conductor industry.
This invention discloses effective stabilizers which can be used to slow down the rate of degradation for the unsaturated hydrocarbons precursors, thereby mitigating the potential process and film quality issues which can result from precursor instability, thus, increasing the viability of such materials for application as precursors for porogens, carbon hardmask materials and antireflective coatings for the production of high quality low dielectric constant films.